Search

The adsorption and reaction of silver on an oxidized Si(0 0 1) surface were investigated on the basis of Si 2p, Ag 3d and O 1s core-level photoemission measurements at room temperature (RT). We compared the present results with those obtained in the case of titanium in our previous study. We found that silver on an oxidized Si(0 0 1) surface at RT causes a reduction in the intensity of the Si 1+ and Si 2+ states and an increase in the intensity of the Si 3+ and Si 4+ states. Based on an analysis of the Ag 3d and O 1s states, we concluded that the change in the Si 2p oxidized states upon silver adsorption is due to charge transfer rather than conformation change, although the applicability of the charge transfer scheme may be dependent on the thickness of the silver layer. We also deduced that penetration of silver atoms through a thin silicon oxide film occurs.

The adsorption and reaction of titanium on an oxidized Si(0 0 1) surface have been investigated using Si 2p, Ti 2p and O 1s core level photoemission measurements at room temperature (RT). We found that titanium adsorption on an oxidized Si(0 0 1) surface at RT causes a reduction of the intensity of the Si1+ and Si2+ states and an increase of the intensity of the Si3+ and Si4+ states. Based on an analysis of the Ti 2p and O 1s states, we conclude that the change in the Si 2p oxidized state upon titanium adsorption is due to charge transfer rather than conformation change.

We have performed synchrotron-radiation angle-resolved photoemission and angle-resolved two-photon photoemission (2PPE) study of Bi(1 1 1) films with the thickness of 12 bilayers grown on Si(1 1 1) – 7 × 7. From the detailed analysis of the excitation energy dependence of angle-resolved 2PPE spectra, we have determined the electronic structures in the occupied and unoccupied regions. The observed electronic structures in the unoccupied states above the Fermi-energy were attributed to the quantum-well states originate from the quantization of the 6p-derived bulk bands.

Time-resolved two-photon photoemission study has been performed on Si(1 1 1) surface at initial oxidation stage that is characterized by synchrotron-radiation photoemission spectroscopy. Transient 2PPE intensity from the conduction band minimum (CBM) shows a maximum at the delay time between 0.5 and 2 ps depending on the oxygen dosage. The temporal profile of 2PPE intensity from surface state within the bulk band-gap shows a more rapid decrease than that on Si(0 0 1) surface, indicating that the metallic surface state on Si(1 1 1) surface causes the shorter lifetime of unoccupied surface state. The prolonged lifetime of 2PPE intensity from CBM after a large amount of O 2 exposure is caused by the disappearance of metallic surface state.

We have investigated the defect formation processes of BaF2 single crystals under vacuum ultraviolet radiation with the use of combination spectroscopy of synchrotron radiation (SR) and laser. The defect formation efficiency was measured as a function of excitation photon energy of SR by means of a laser-induced luminescence method. It was found that the efficiency depends significantly on the excitation photon energy. We show that the dependence can be explained in terms of the diffusive motion of hot conduction electrons generated by the photoexcitation. The relationship between the defect formation and the energy relaxation of core excitons is also discussed.

We have studied the electronic structure within the topmost two quintuple layers (QL) on vacuum-cleaved n- and p-type Bi2Te3(111) at 10 K by angle-resolved photoelectron spectroscopy. Tunable synchrotron radiation maximized the surface sensitivity of photoelectrons. The gapless surface-state band (SSB) in the angle-resolved photoelectron spectra clearly demonstrates the topological nature of the samples. Below the SSB, the bulk valence bands (BVB) is observed. Against the three-fold symmetry of the crystal structure, the k|| dispersion of the BVB is highly symmetrical around the Γ, which indicates the six-fold symmetry. Moreover, most of the BVB show almost flat k⊥ dispersion perpendicular to the surface. These facts are the experimental evidence of a strong modification of the valence bands within the topmost two QLs into highly two-dimensional states by the advent of the surface. [DOI: 10.1380/ejssnt.2012.117]

The excited electronic states on Si(0 0 1) surface at the initial stage of oxidation have been studied by time-resolved two-photon photoemission (2PPE) spectroscopy. Transient 2PPE intensity from the conduction band minimum (CBM) shows the maximum at about 1 ps after a direct excitation from bulk valence- to conduction-band. This is due to accumulation of photo-excited electrons to CBM by the intraband scattering. The 2PPE signal around 0.6 eV below CBM shows a maximum intensity at around 10 ps. It can be considered that this 2PPE intensity originates from the unoccupied state derived from surface oxide. Electrons at both CBM and oxide state show longer lifetimes as oxidation proceeds.

Metal–organic interfaces have been attracting continuous attention in many fields including basic biosciences. The surface of dental alloys could be one of such interfaces since they are used in a circumstance full of organic compounds such as proteins and bacteria. In this work, electronic structures of Au-dominant dental alloys, which have Ag and Cu besides Au, and those of l -cysteine on the dental alloys have been studied by photoelectron spectroscopy with synchrotron radiation. It was found that the density of states in the dental alloy originate from gold and copper as constituents, and the Cu-3d states contribute dominantly to the occupied states near the Fermi level. It was also found that the electronic structure of the l -cysteine thin film on the dental alloy is different from that of the l -cysteine thick film. The result indicates the formation of the orbital bonding between Cu-3d and S-3sp states in the thin film on the dental alloy.

An ultrathin and super black amorphous carbon (a-C) film has been fabricated by borrowing the inverse V-type anti-reflection nano-architecture from the black wings of butterfly Ornithoptera goliath through vacuum sintering process. The biomimetic a-C film shows good optical absorption (99%) at low reflectance (

Valence electronic structure of β - FeSi 2 single crystal has been investigated by photoelectron spectroscopy using synchrotron radiation. The plate-type β - FeSi 2 single crystal has been grown by chemical vapor transport method. The surface contamination and oxide layer were removed by Ne+ ion sputtering. The dependence of the valence band spectra on exciting photon energy shows that the strong peak at the binging energy ( E Bin ) of 0.5 eV and the shoulder peak at E Bin = 8 eV are assigned to be Fe 3 d and Si 3 p orbitals, respectively. Upon the excitation of Fe 2 p 3 / 2 , resonant enhancement of the valence band was observed at E Bin = 3.7 eV, which is very similar to Fe metal. This fact suggests the existence of the two-hole satellite states from Fe 3 d orbitals.

Dynamics of the photo-excited carriers on the GaAs(100) surface have been studied by measuring the surface photo-voltage effect (SPV) with the ultrafast time-resolved photoemission spectroscopy. The fast SPV decay with a few picosecond lifetime has been observed on the n -type GaAs(100) surface. The lifetime of the fast decay component was almost independent with dopant levels, pump powers, and sample temperatures which mainly change the surface potential barrier in the band bending region. This result supports the SPV relaxation model of the hot electron because the time scale of the electron thermalization is considered to be less affected by the change of the surface potential barrier. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The soft X-ray beamline constructed for an industry application is briefly introduced. The varied line spacing plane grating monochromator (VLS-PGM) has been designed in order to cover the wide-energy range from 40-1000 eV with a set of three focusing mirrors and one grating. The resolving power is expected to be more than 5000 with 10 micron slits. The conventional photoelectron spectrometer is installed with an ion gun, a flood gun and a twinanode X-ray source. The instrument for XAFS measurement is also attached to the main chamber.

A unique analytical method is proposed for local structure analysisviaextended X-ray absorption fine structure (EXAFS) spectroscopy. The measurement of electron energy distribution curves at various excitation photon energies using an electron energy analyzer is applied to determine a specific elemental Auger spectrum. To demonstrate the method, the NK-edge EXAFS spectra for a silicon nitride film were obtainedviasimultaneous measurement of the NKLLAuger and background spectra using dual-energy windows. The background spectrum was then used to remove the photoelectrons and secondary electron mixing in the energy distribution curves. The spectrum obtained following this subtraction procedure represents the `true' NK-edge EXAFS spectrum without the other absorptions that are observed in total electron yield NK-edge EXAFS spectra. The first nearest-neighbor distance (N—Si) derived from the extracted NK-edge EXAFS oscillation was in good agreement with the value derived from SiK-edge analysis. This result confirmed that the present method, referred to as differential electron yield (DEY)-EXAFS, is valid for deriving local surface structure information for low-Zelements.

The Drude tail due to photo-excited carriers in single-walled carbon nanotubes (SWNTs) has been observed in the mid-infrared region by using combination spectroscopy of synchrotron radiation and Ti:sapphire laser. It is found that the density of photo-excited carriers increases as the sample temperature is raised from 12 to 300 K, and their lifetime is of the order of minutes at 300 K. These facts suggest that the movement of photo-excited carriers is largely affected by some extrinsic defect, thus resulting in the long-lasting Drude reflection in SWNTs.

Transient infrared absorption measurements are performed to study the photo-induced states in PbWO4 crystals at 16 K. A broad band is observed above 4000 cm−1, with a peak around 9000 cm−1. This band has a lifetime of 50 ms at 16 K, and disappears when the sample temperature is increased above 25 K. To investigate the origin of the photo-induced states, thermoluminescence is also measured after prolonged irradiation with 7.7-eV light at 8 K. Three glow peaks are observed at 15, 30, and 53 K. It is pointed out that the photo-induced band has a correlation with the 15-K glow peak, and is attributed to the (WO4)3− complex perturbed by another defect at the nearest-neighbor site.

A new beamline for high-resolution angle-resolved photoemission study on solids and surfaces has been constructed at BL13 of Saga Light Source. In order to realize high-resolution in a wide energy range, the monochromator system is composed of the grazing-incidence mount with two varied line spacing plane gratings (VLSPG) and the normal incidence mount with a multilayer-coated plane grating. Relatively, high photon flux and low higher-order light can be obtained using the multilayer-coated plane grating in the boundary region between grazing-incidence and normal-incidence mounts. It is found from ray-tracing simulations that resolving power better than 10,000 and photon flux of 10 10 –10 12 photon/s can be obtained. A high-resolution photoemission system with a gated-detector and a mode-locked Ti:Sapphire laser with the regenerative amplifier is installed at the beamline. Using these systems, we can perform the time-resolved high-resolution photoemission study for various photo-excited phenomena and surface dynamics.

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs–GaAsP superlattice (SL) were measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. It was found that the SPV effect in the SL is remarkably suppressed as compared with that in a bulk GaAs. The difference in the temporal profile of the SPV between SL and bulk samples was observed in microsecond range. The suppression of the SPV effect in the negative electron affinity surfaces of the SL was also observed. It is concluded that the SL with a high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.

Core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser light was used for exploring the dynamics of the surface photovoltage (SPV) effect on a p -GaAs (100). It was found that a temporal profile of the SPV is very different in microsecond range between room temperature and 90 K. The results can be explained with the recombination of photoexcited carriers via thermionic and tunneling processes. The SPV effects and its temporal profiles on the negative electron-affinity (NEA) surface were also studied. It was observed that the SPV effect is suppressed on the NEA surface, which may be due to the escape process of the photoexcited carriers.

The Sn 4d and Pb 5d core-level photoelectron spectra have been studied in order to clarify their bonding properties and atomic arrangement on a Si(1 1 1) √7×√3-(Pb, Sn) surface, which is formed by the coadsorption of 0.4 ML Pb and 0.4 ML Sn and shows two kinds of bright spots in the scanning tunneling microscopic (STM) images: (A) those aligned zigzag on the T1 site and (B) those on the T1 and H3 sites along the [1 1 −2] direction. The Pb 5d spectrum shows a single spin–orbit-split feature with weak tailing towards the high binding energy side, while the Sn 4d spectrum exhibits shoulder structures at the high binding energy side of the main peaks. This definitely indicates at least two different Sn–Si bonds or inequivalent Sn adsorbing sites and single bond or site for Pb. Thus the spots A at the T1 site and those B at the T1 and H3 sites in the STM images are ascribed to Pb and Sn adatoms, respectively. The formation process of this surface will be also discussed in terms of the core-level spectra.

Reflection spectra of polyethylene terephthalate (PET) and polyethylene naphthalate films were measured for 50 to 600 nm, using a Seya–Namioka type monochromator at UVSOR, and were converted into absorption spectra by Kramers–Kronig formula. Dichroic nature of drawn films was clearly displayed in the whole region. Previous analysis was confirmed to be true that the third absorption peak of PET, which appeared in the limit of atmospheric measurement, consisted of two peaks of different polarization. Their VI and VII absorption bands at 13.3–15.5 eV originated in transitions associated with r electrons, and had absorption coefficients of 1:1–1:3 � 10 6 cm � 1 .

An Si(1 1 1)2√7×3-(Pb,Sn) surface was studied by means of scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES) to identify its electronic structure. The dispersion relationships along the [1 0 1 ] direction and [ 1 2 1 ] direction were obtained by ARPES and two surface states of S1 and S2 were clearly observed on the 2√7×3-(Pb,Sn) surface. There was no surface band across the Fermi level and the dispersion of both surface states S1 and S2 were rather flat. The S1 band had peaks at Γ and K points, and the S2 band had a maximum at M point. The periodicity of S1 band did not match both 2√7×3 and 1×1 surface Brillouin zones. STM images of the 2√7×3-(Pb,Sn) surface showed bright spot arrays and continuous bright lines that exhibit 1D charge density wave along [1 0 1 ] direction for both empty and filled states. The 2√7×3-(Pb,Sn) surface intrinsically has domain boundary. The surface states S1 and S2 seem to correspond to the bright spot arrays and continuous bright lines, respectively.

X-ray and ultra-violet photoemission spectra have been measured to study the valence-band structures of piperidinium trihaloplumbates C 5 H 10 NH 2 PbX 3 [X = I, Br], which have natural nano-scale ...

This work is an investigation of the desorption by O 1s excitation of ions from Si(100) reacted with water. Photoelectron, photostimulated desorption, and electron-ion coincidence spectroscopy are used to observe the process. When the incident photons have energy levels which are near the 1s threshold of O, they induce Auger decay that is accompanied by shakeup/off excitation and cascade Auger decay, and they are shown to be the main factor responsible for desorption in this case. When the photons have energy levels which are above the shakeup threshold, most of the desorption that occurs is a result of the shakeup excitation that accompanies the core excitation. In both cases, the desorption is induced by the respective multihole final states. The ion desorption yield for the two-hole final states of the normal process of Auger decay is small. The results are discussed, with the help of the Auger electron spectra, mainly in terms of the lifetime of the final state of Auger decay.

The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.

The nonradiative decay processes of the Ba -5p core exciton in BaF 2 have been investigated by using photoelectron spectroscopy, since the exciton peak is missing in the excitation spectrum of the Auger-free luminescence. The decay probability of the direct recombination process estimated from the constant-initial state spectrum and the absorption coefficient was found to be smaller than unity, indicating the existence of the other decay processes. It is suggested that the Ba -5p core exciton is relaxed by about 0.9 eV.

The new experimental systems for investigating the photo-induced phenomena have been constructed. They consist of the photoelectron spectroscopy system based on the synchrotron radiation, the laser system based on the mode-locked pulse lasers, and the experimental system for time-resolved measurements. The systems have been applied to study the surface photo-voltage (SPV) effects on the surfaces of GaAs (100) and GaAs-GaAsP superlattice. The results showed that the temporal profiles of the surface photo-voltage effects have several components in the nano- and micro-second ranges, which depend on the surface conditions.

Image potential states (IPSs) on monolayer, bilayer, and trilayer graphene epitaxially grown on SiC(0001) have been studied by time- and angle-resolved two-photon photoemission (2PPE) spectroscopy. The free-electron-like dispersions of even and odd symmetry IPSs with a quantum number of $n$ = 1${}^{+}$, 1${}^{\ensuremath{-}}$, 2, 3 were observed. All observed IPSs showed the dispersions with effective masses of ${m}^{*}=1.0\ifmmode\pm\else\textpm\fi{}0.1{m}_{e}$. The 2PPE intensity of the lowest IPS ($n$ = 1${}^{+}$) was attenuated with an increasing number of graphene layers. The time-resolved 2PPE measurements revealed that these IPSs have significantly shorter lifetimes, suggesting a coupling of IPSs with electronic states in the buffer layer and the SiC substrate.

The line shape of Auger-free luminescence (AFL), caused by radiative recombination of holes in the outermost-core band with valence electrons, has been studied for CsCl, CsBr and BaF 2 in comparison to photoelectron spectra of the valence bands. It is confirmed that the main part of AFL locates on the low-energy side of the valence-band region estimated from the maximum of the outermost-core band in the photoelectron spectra. Furthermore, its low-energy tail extends by approximately 0.5–1.0 eV below the minimum of the valence band. These results clearly indicate that the core hole induces considerable lattice distortion around itself, which is kept well during the radiative transition. The line shape of AFL is favorably explained in terms of an energy-band picture in which the lattice relaxation is taken into account in principle.

The (4 d →6 p )-core exciton and its decay on Xe film has been investigated with partial and total electron yield spectroscopy and photoelectron spectroscopy. The energy shift between the surface and bulk core exiton has been determined to be −0.2 eV. The interaction energies between the core hole and the excited electron have been estimated for bulk, surface and gaseous Xe. Using resonant Auger electron spectroscopy, a spectator Auger feature has been observed in the decay of the surface core exciton. This contrasts to the spectrum of the decay of the bulk core exciton which shows predominantly normal Auger features.

The optical and electric properties of an l-cysteine film have been investigated to understand its applicability to bioelectronics. The fundamental absorption is the allowed transition having the threshold at 5.8 eV and the absorption is due to the charge-transfer type transition from sulfur-3sp to oxygen-2p and/or carbon-2p states, while absorptions more than 9 eV can be explained with intra-atomic transitions in the functional groups. The electric resistivity is 2.0 × 104 Ω m at room temperature and increases as the sample temperature decreases. The results indicate that the l-cysteine film is a p-type semiconductor showing the hole conduction caused by the sulfur-3sp occupied states and unknown impurity or defect states as acceptors. The electron affinity of the l-cysteine film is derived as ≦−0.3 eV.

Biological systems have complicated hierarchical architecture involving nano-structures inside, and are expected as another candidate for new nano-templates. The present work reports the photoelectron spectroscopic study on electronic structure of the butterfly-templated ZnO that were successfully produced from butterfly wings. Ultraviolet Photoelectron Spectrum (UPS) of the butterfly-templated ZnO shows clearly the valence band and a Zn-3d peak, indicating that the butterfly-templated ZnO has the same electronic structure as bulk ZnO. However, the detailes show that the energy positions of the Zn-3d level and the valence-band structure are different between them. The present results indicate that the bonding interaction between Zn-4sp and O-2p orbitals is stronger in the butterfly-templated ZnO, probably due to the nano-structures inside. Important parameters such as band bending and electron affinity are also obtained. The larger band bending and the lower electron affinity are found in the butterfly-templated ZnO (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Production of radiation defects in a widely used scintillation material BaF 2 has been studied by means of a combination spectroscopy of synchrotron radiation (SR) and laser, in which defects produced by SR irradiation are sensitively detected by observing the luminescence stimulated by laser light. The photostimulated luminescence arises from the recombination of self-trapped holes (V K centers) with electrons released from trapped centers by laser light. The obtained result reveals that the production efficiency of radiation defects is drastically dependent on the excitation photon energy of valence or core excitons.

The orientation of oxygen ad-molecules was examined on stepped Pt(112)=(s)[3(111)×(001)] at around 110 K by means of near-edge extended X-ray absorption fine-structure (NEXAFS). The π ∗ resonance was always major when the electric vector of the incident X-ray was in a plane perpendicular to the step edge. On the other hand, when the vector was in the plane parallel to it, the σ ∗ resonance was major at the normal incidence and was attenuated with increasing incidence angle of the X-ray whereas the π ∗ resonance was enhanced. It was concluded that oxygen was mostly oriented along the step edge.

The photo-induced change in the semiconductor–vacuum interface on GaAs(100) and Cs/GaAs(100) has been investigated with core-level photoelectron spectroscopy using synchrotron radiation and a mode-locked Nd:YAG laser. Both Ga-3d and As-3d photoelectron peaks showed transient energy shifts under the laser irradiation without any spectral change. The amounts of energy shift were strongly dependent on the sample temperature and laser photon flux. It is shown that the experimental results can be fitted to a theoretical curve which was derived from the photo-induced band bending scheme in the surface layer of the semiconductor.

Photo-stimulated desorption from the TiO 2 (110) surface was investigated by using electron–ion coincidence spectroscopy and synchrotron radiation. The desorption of O + ions was observed to be coincident with the emission of photoelectrons from the O 1s, Ti 2s, Ti 2p, Ti 3s and Ti 3p levels, and their satellite peaks due to the shake-up excitation. However, no ion desorption was observed in coincidence with the O 2s or valence photoelectrons. The O + peak intensities in the coincidence spectra are analyzed, and the result is unexpected from a simple expansion of the Knotek–Feibelman model. The shake-up excitation of O 1s levels yields O + desorption more efficiently than does the O 1s single-electron excitation.

The paper presents the results of experimental studies aimed at testing the amplification of impurity-associated Auger-free luminescence (275 nm band) in mixed rubidium–caesium chloride crystals under core-level excitation with undulator radiation. The emission features observed under the best collimation of the optical cavity, namely the enhancement of the peak intensity, the sharpening of the emission spectrum and the shortening of the luminescence decay, suggest a possibility of the light amplification due to inverted population between the valence and 5pCs-impurity core states. A further lasing performance with regard to possibilities for development of this technique is also briefly discussed.

Exciton states in wide-gap materials CaF2 and BaF2 have been studied with the technique of two-photon spectroscopy using synchrotron radiation and laser. The two-photon excitation spectrum of CaF2, and that of BaF2 as well, exhibited a clear peak on the high-energy side of the 1 S exciton energy. The peaks are attributed to the 2 P states of the valence excitons. According to this assignment, the binding energies of the excitons have been determined to be 0.8 and 0.9 eV for CaF2 and BaF2, respectively. The signal intensities were larger than that in the case of one-beam excitation by a factor of about 500, which is attributed to a resonant effect on two-photon absorption. @S0163-1829~99!52836-1#

Desorption of the excited-state alkali atoms has been investigated on alkali fluoride crystals in the photon energy region of 20–75 eV, which includes the excitation energy for Li 1s-core excitons, Na 2p-core excitons, and valence excitations. The quantum yield of the excited-state alkali desorption was found to be comparable between valence and core-level excitations. Time response of desorption from LiF and NaF was also observed by using synchrotron radiation pulses. It was found that the time response consists of a nanosecond component and slower one, indicating that the fast desorption is due to the lattice instability induced by electronic transition and the slow one is due to the thermal instability of surface defects.

Oxygen admolecules on stepped Pt(133)=(s)[3(111)×(111)] were characterized by means of thermal desorption spectroscopy and near-edge X-ray absorption fine structure. Three admolecule desorption peaks were found at 150 K (α3-O2), 175 K (α2-O2) and 220 K (α1-O2). The admolecules yielding α1-O2 lie along surface troughs, whereas those yielding α2-O2 and α3-O2 lie on declining (111) terraces and are largely rotated from the surface trough direction. The rotation angles were estimated to be 40±10° for α2-O2 and 60±10° for α3-O2. These values were determined by comparing experimental X-ray incident angle dependence of π* and σ* resonances with simple simulated calculations. These oriented admolecules can be selectively prepared on this surface.

In situ high-pressure measurements of the far-infrared absorption spectra in ice VII and VIII covering the region of translational lattice modes are made by utilizing an infrared beam line of synchrotron radiation at the Institute for Molecular Science (Okazaki). Although the lattice dynamics are almost same for both the phases, large spectral changes are observed on the occasion of the proton order-disorder transition. In the proton disordered phase (ice VII), absorption spectra reflecting a density of states of lattice modes are obtained. The proton ordered phase (ice VIII) gives rise to an absorption peak due to the optical phonon at the r point. The anomalous pressure dependence of the phonon energy in ice VIII indicates the occurrence of a lattice instability below 2.7 GPa with decreasing pressure, which is supported by the recent neutron inelastic scattering experiments by Besson et al.

The migration of the core exciton in a mixed crystal of Rb 0.82 Cs 0.18 Cl is investigated through time-resolved measurement under excitation with synchrotron radiation (SR) and laser. The photon energy of SR is tuned to the absorption band due to the exciton composed of a conduction electron and the hole originated from the outermost core state of the Rb ion (Rb-core exciton). The time-integrated intensity of Auger-free luminescence (AFL) due to the outermost core state of the Cs ion is increased by the laser irradiation. The lifetime of the laser-induced AFL depends on the photon energy of SR. The experimental result suggests the difference between the migration length of the Rb-core exciton and that of the Cs-core hole.

Oxygen admolecules on stepped Pt(133)=(s)3(111)×(111) were characterized by thermal desorption spectroscopy and near-edge X-ray absorption fine structure. Three admolecule desorption peaks were found at 150 K (α3-O2), 175 K (α2-O2) and 220 K (α1-O2). The admolecule yielding α1-O2 lies along the trough, whereas α2-O2 and α3-O2 lie on declining (111) terraces and are inclined about 35° and 50° from the trough direction, respectively.

The electronic structure of a Na/Ge(111)- surface was investigated by valence-band and core-level photoemission spectroscopy with synchrotron radiation. The two-dimensional energy-band dispersion of the surface Brillouin zone along was mapped out. The experimental surface-state dispersions show a better agreement with the theoretical results for the buckled Seiwatz model than the extended Pandey model. The surface core-level shift of the surface is explained on the basis of the buckled Seiwatz model. The surface reveals more covalent bonding character than other Na-adsorbed surfaces at room temperature, and its surface Fermi level is close to the valence-band maximum.

We have carried out nonlinear spectroscopy by making use of tunable VUV light from synchrotron radiation (SR) together with intense light from a laser. The valence excitons of BaF 2 with a large band gap of ∼11 eV were chosen as our target. A single crystal of BaF 2 was irradiated at 15 K by the two light pulses from the SR (6–9 eV) and an Nd : YAG laser (2.33 eV). Self-trapped exciton luminescence induced by two-photon excitation was detected with a time-gated photon-counting system developed for the present study. This zero-method technique is expected to be sensitive compared to early experiments by an Italian group monitoring transmittance changes. The obtained two-photon spectrum shows a distinct band below the band gap energy. This band includes two contributions, a two-step cascade process and a two-photon absorption process. The energy of the 2 P exciton is estimated to be 10.6 eV at 15 K.

The circular dichroism of angle-resolved photoelectron spectra was investigated for core-levels from clean and hydrogen exposed GaAs (111) surfaces. It was found that the circular dichroism of Ga-3d and As-3d photoelectrons shows clear dependence on the emission angle of the photoelectrons and the sample surface. It is proposed that the experimental results may be interpreted primarily in terms of the interference of photoelectrons affected by the anisotropic field in the surface layer of GaAs (111).

Photoelectron and optical spectra are both important in order to know the electronic structures of solids, but they have only been measured independently in insulating materials so far. In the present experiments, simultaneous measurements of photoelectron and luminescence spectra of BaF2 thin films were carried out. It was found that both photoemission and luminescence intensities decrease with increasing synchrotron-radiation doses, indicating the formation of radiation-induced defects. Also, the time correlation between Ba-4d photoelectrons and Auger-free luminescence photons was observed for the first time, suggesting that these two processes correlate with each other.